Bushing insulator



Jan. 30, 1940. H, L, RQRDEN 2,188,417

' BUSHING INSULATOR Filed Feb. 4, 1938 2 Sheets-Sheet 1 w INVENTOR 56 vHare/0 L. fora m7 BYWJ- ATTORNEY Jan. 30, 1940. H. RORDEN BUSHINGINSULATOR 2 Sheets-Sheet 2 Filed Feb. 4, 1938 INVENTOR //4/0/0 L. fin)?/fi ATTORNEY Patented Jan. 30, 1940 UNITED STATES PATENT OFFICE BUSHINGINSULATOR Harold L. Borden, Barberton, Ohio, assignor to I The OhioBrass Company, Mansfield, Ohio, a corporation of New. Jersey ApplicationFebruary 4, 1938, Serial No. 188,691

7 Claims.

. mum.

A further object of the invention is to provide a bushing insulator in.which the danger of overstressing the insulating liquid is also reducedto a minimum.

A further object of the invention is to provide a bushing insulatorhaving a plurality of baffles with means for improving the voltagegradient in the insulation.

A further object of the invention is to provide a device of the classnamed which shall be of improved construction and operation.

Other objects and advantages will appear from the following description.

The invention is exemplified by the combination and arrangement of partsshown in the accompanying drawings and described in the followingspecification and' it is more particularly pointed in the appendedclaims.

In the drawings:

Fig. 1 is an elevation of a bushing insulator with parts in sectionshowing one embodiment of the present invention.

Figs. 2 and 3 are fragmentary sections showing modifications of theinvention.

Fig. 4 is a view similar to Fig. 1 showing another form of theinvention.

Figs. 5, 6, 7 and 8 are fragmentary sections of bushing insulatorsshowing their modified features of the invention.

In the form of the invention shown in Fig. 1 the number I!) designates ahollow conductor extending through a flange arranged to be connected toan opening in a housing for electrical apparatus such as a switchhousing or a housing for a transformer. At the lower end of theconductor H! is a fitting l2 secured to the conductor and supporting thelower dome |3 of the bushing insulator. The dome |3 is preferably madeof porcelain but may be made of other suitable insulating material. Ashoulder |4 extends outwardly from the upper portion of the dome I 3 andsupports the flange I. The cone l5 rests on the flange H and carries anexpansion chamber I6. Within the expansion chamber I6 is a compressionspring H which supports a ring l8 which engages a collar l9 secured tothe upper space within the bushing. Sufiicient slippage is end of theconductor Il The spring exerts a tension on the conductor I0 and acompression on the dome l3, cone l5 and flange I I, thus holding theparts of the insulator together. Secured to the lower end of theconductor I0 is a fitting 5 2|] which carries a porcelain baffle tube 2|surrounding the conductor II]. A second porcelain baflle 22 is securedto the baflle 2| by cement joints 23 and 24. The dome l3 is providedwith an extension 25 which projects through the flange 10.

|| so as to increase the insulation between the conductor I0 and theflange. The space within the bushing not otherwise occupied ispreferably filled with insulating oil or other dielectric liquid and theinner space 26 immediately surrounding 15- the conductor I0 ispreferably separated from the remainder of the space within the bushingby the battle 2| and a metal tube 21 which is secured to the upper endof the bafile 2| by a liquid tight joint at 28. The inner face of thetube 2| is preferably coated with conducting material 29. This coatingmay be made of copper or other suitable metal sprayed upon the innersurface of the tube. There are several well known methods for coatingporcelain with metal any one of which may be used for this purpose. Apassage 3|] extends through the fitting an to connect the space 26 withthe remainder of the space within the bushing. The gasket 3| isinterposed between the expansion chamber l6 and the cone |5 to 30 form aliquid tight joint at this point and the inner edge of the gasket bearsagainst the tube 21 with suflicient force to prevent circulation of theoil from the expansion chamber to the outer permitted, however, toprevent stress due to differential expansion of the bushing parts. Whenthe bushing and the expansion chamber are filled with oil, the oil willexpand and contract due to temperature changes, producing a breathingaction through the upper portion of the expansion chamber. This willpermit the oil in the expansion chamber to contact with the air which isbreathed into the chamber and some of the moisture or othercontamination in the air may be absorbed by the oil in the expansionchamber. This oil, however, is not in direct contact with the main bodyof the oil in the bushing, but is separated from the main body by thetube 21 and the baffle 2!. The space immediately surrounding theconductor I0 is of sufiicient volume that the contaminated oil in theexpansion chamber will never be drawn through the passage 30 into thespace outside the bafile 2|. Deterioration of the oil in the space 26 isof no serious consequence because this space is preferably shunted by ajumper 32 so that even if the oil in the space 26 is not a perfectdielectric, there will be no breakdown of the oil in this region becauseit is not subjected to electric voltage. It has been found advantageousto provide a shunt across this space to prevent overstress of the. oileven when the oil is not contaminated, because, where the space 26 isnot shunted, it is subject to a very high voltage due to the fact thatelectrostatic lines of force are concentrated in this zone adjacent theconductor; and also due to the fact that oil has -a lower specificinductive capacity than porcelain and consequently, there is a greaterdrop of potential through the oil than there would be through a likethickness of porcelain. The coating 29 and jumper 32, therefore, performa double function of short-circuiting the zone of highest electrical.stress and the zone most apt to contain oil which has been affected bycontact with the outer atmosphere.

By extending the dome |3 through the flange 1, additional insulation isprovided between the conductor and the flange to compensate for theshunted space 26 about the conductor. This insulation is moreadvantageously placed than the oil in the space 25 because of thegreater area at the greater distance from the axis of the conductor. Bythis arrangement the voltage stress is allocated in the portion of theinsulator farther removed from the axis and in a zone where the lines offorce are less concentrated so that the dielectric is more effective inwithstanding the voltage.

In order to reduce the danger of corona or arcing from the flange towardthe expansion chamber, ap'ocket 33 is provided in the lower portion ofthe cone l5 and the inner surface of the pocket is metallized andconnected with the flange so that the electrostatic lines of force willemanate from the lining of the pocket directly into the porcelain andnot into the atmosphere.

The form of the invention shown in Fig. 2 is similar to that in Fig. 1except that the baffles 2| and 22 are both metallized on both theirinner and outer faces, there being suflicient space at the ends of thebattles which is not coated to prevent discharge aboutthe ends of theb'aflles'. The adjacent coatings are connected by jumpers 35 and 35.thusshunting the oil space between the baiiles and placing the entirevoltage stress upon the porcelain. The conductor plates thus providedbetween the porcelain baffles forms 'a condenser arrangementwhichassists in producing a better voltage gradient between theconductor Hi and the flange H.

In the form of the invention shown in Fig. 3 the upper portion of theouter surface of the dome i3 is metallized as shown at 36, the loweredge of the metal coating terminating in a pocket 3'! forming a fluxcontrol for preventing electrostatic discharge at the lower edge of thecoating 318. The flux control 31 is preferably located far enough downon the dome I3 so that it will be always submerged in the insulatingfluid in the housing for the electrical apparatus served by the bushing.This prevents any danger of discharge downwardly from the flange II.

In the form of invention shown in Fig. i the dome l3 terminates at theflange H and an additional keg 33 is carried by the flange within theouter shell of the bushing to help withstand the voltage between theconductor and the flange. In this form of the invention, instead ofutilizing air out through the tube 4|.

the inner porcelain baffle 2| to divide the oil space within thebushing, a special metal tube 39 surrounds the conductor ID and isflared outwardly at its upper end to form a flange 40 which is caughtbetween the upper end of the cone I5 and the expansion chamber I6forming a tight joint at this point. A small tube 4| extends through thewall of the tube 39 and projects upwardly inside of the conductor !0 toa point where it communicates with the outer atmosphere. This permitsescape of air from the space within the bushing surrounding the tube 39as oil is filled into. the bushing. The oil will flow down in the space26 between the conductor and the tube 3 9 and enter the outer portion ofthe bushing through the passage 39 forcing the The space 26 between theconductor Hi and the tube 39 is sufficient to accommodate the ebb andflow of the oil due to any breathing action so that contamination due tocontact with the outer atmosphere will not affect the oil outside of thetube 39.

Fig. 5 shows a difierent arrangement for permitting escape of air fromthe outer portion of the bushing when the bushing is being filled withoil. In place of the. tube 4| a valve 42 permits escape of air from theouter portion of the bushing'but prevents entrance of oil into thebushing directly from the expansion chamber.

In the form of invention shown in Fig. 6 a metal tube 43 is soldered tothe metal coating 29 on the bafiie 2| and has its upper end turnedoutwardly and caught beneath the expansion chamber I6 as shown at 44. Atube 45 similar to the tube 4| in Fig. 4 connects the space outside ofthe battle 2 with the outer atmosphere to permit escape of air when thebushing is filled with oil. i g

In the form of invention shown in Fig. 7 a tube 56 is soldered to thebattle 2| and extends past a gasket 3| asin Fig. 1. In this case thespace within the expansion chamber communicates with the upper end ofthe tube 46 through a passage 41 which is elevated somewhat above thebottom of the expansion chamber providing a sump. 48 for theaccumulation of moisture which may be entrapped by the oil in theexpansion chamber. v

A similar trap 49 may be formed at the lower end of the tube 39 as shownin Fig. 8 by closing the lower end of the tube by means of packing 50and providing an opening 5| for the escape of oil into the outer portionof the bushing at a point somewhat above the lower end of the tube 39.

I claim:

1. The combination with an electrode having an opening therethrough anda conductorextending through said opening, of a bushing insulatorseparating said conductor from said electrode, said bushing insulatorcomprising a housing having space therein closed at its bottom, electricinsulation within said space including an insulating liquid, said spacebeing divided into inner and outer compartments, the dominant insulationin said space between said electrode and conductor being disposed insaid outer compartment, the liquid in said inner compartment having itssurface exposed to atmospheric pressure, said compartments being sealedagainst communication with each other at their upper ends but connectedat their lower ends and being constructed and arranged so that thedominant portion of all liquidentering said outer compartment t0compensate-rfor, contraction of the liquid in said outer compartmentwill be supplied from the inner compartment, said inner compartmenthaving suilicient capacity between the surface of the liquid therein andthe point of communication between said compartments to accommodate theebb and flow of the insulating liquid due to expansion and contractionof the liquid in said outer compartment without passage from said innerto said outer compartment of liquid which has been contaminated bycontact with the atmosphere.

2. In combination. a bushing insulator comprising a housing, anexpansion chamber communicating with the outer atmosphere and con nectedwith said housing, a conductor extending through said housing and havingliquid tight connection with said housing at the lower end of saidhousing and a baffle tube surrounding said conductor and communicatingat its upper end With said expansion chamber and at its lower end withthe interior of said housing outside of said baflie tube and dividingthe interior of said housing into inner and outer compartments, saidbafiie tube at its upper end forming a liquid tight partition betweenthe upper portions of said compartments and preventing direct passage ofsaid insulating liquid from said expansion chamber to said outercompartment, the inner and outer walls of said outer compartment beinginsulated from each other so that insulating liquid in said outercompartment forms an effective portion of the bushing insulation.

3. In a bushing insulator, a dielectric housing, a conductor extendingthrough said housing, the space within said housing being closed againstescape of liquid through the bottom of said housing, an expansionchamber at one end of said housing, and a tube surrounding saidconductor and communicating at one end with said expansion chamber andat the other end with the space within said housing outside of said tubefor preventing direct passage oi insulating liquid from said expansionchamber to the space within said housing outside of said tube, saidspace having outer and inner walls insulated from each other.

4. In a bushing insulator, a dielectric housing, a conductor extendingthrough said housing, the space within said housing being closed againstescape of liquid through the bottom of said housing, an expansionchamber at one end of said housing and communicating with the outeratmosphere, a tube surrounding said conductor and communicating withsaid expansion chamber and separating the space immediately adjacentsaid conductor from the space outside of said tube and means separatingsaid outside space from said expansion chamber to prevent oil frompassing directly from said expansion chamber to said outside space, saidtube communicating with said outside space at the end thereof oppositesaid expansion chamber, the inner surface of said tube being conductingand being electrically connected with said conductor to shunt the spacebetween said tube and conductor, said outside space having inner andouter walls insulated from each other.

5. In a bushing insulator a dielectric housing, a conductor extendingthrough said housing, the space within said housing being closed againstescape of liquid through the bottom of said housing, a dielectric bafiietube surrounding said conductor, a conductive coating on the innersurface of said bafile tube, an expansion chamber on said housing andcommunicating with the interior of said baiiie tube, means forpreventing direct communication between said expansion chamber and thespace Within said housing outside of said balile tube, said expansionchamber communicating with said outside space through the space betweensaid conductor and the wall of said baffie tube and means forelectrically connecting said conductor with the conductor coating on theinterior of said baffle tube to shunt the space between said conductorand the wall of said bafile tube, said outside space having inner andouter walls insulated from each other.

6. In combination a bushing insulator comprising an insulator housing, aconductor extending through said housing, the space within said housingbeing closed against escape of liquid through the bottom of saidhousing, an expansion chamber disposed on top of said housing, a bafiletube surrounding said conductor and communicating at its upper end withsaid expansion chamber and at its lower end with the space within saidhousing outside of said tube, said baflle tube providing communicationbetween said expansion chamber and the space within said insulatoroutside of said tube, said space being otherwise completely sealedagainst passage of liquid to and from said expansion chamber, insulatingliquid filling said insulator and extending into said expansion chamber,the space within said insulator outside of said tube having inner andouter walls which are insulated from each other so that the insulatingliquid within said space forms an eifective part of the bushinginsulation.

'7. In combination a bushing insulator housing, a conductor extendingthrough said housing, an expansion chamber at the upper end of saidhousing, a battle tube surrounding said conductor and communicating atits upper end with said expansion chamber and at its lower end with thespace within said housing outside of said tube, the space within saidhousing being closed against escape of liquid through the bottom of saidhousing, the point of communication between the upper end of said tubeand said expansion chamber being located above the bottom of saidexpansion chamber and the wall of said tube having liquid tightconnection with the bottom of said expansion chamber and forming aliquid tight seal between said expansion chamber and the upper end ofthe space within said housing outside of said tube to provide a watertrap in the bottom portion of said expan sion chamber separated fromsaidoutside space.

HAROLD L. RORDEN.

